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We determined the relative expression levels of the receptors TrkA, TrkB, TrkC, and p75NTR and ligands BDNF, NT-3, NGF, and NT-4 with RNAseq analysis on fetal human inner ear samples, located TrkB and TrkC proteins, and quantified BDNF with in situ hybridization on histological sections between gestational weeks (GW) 9 to 19. Spiral ganglion neurons (SGNs) and satellite glia appear to be the main source of BDNF and synthesis peaks twice at GW10 and GW15–GW17. Tonotopical gradients of BDNF revert between GW8 and GW15 and follow a maturation and innervation density gradient in SGNs. NT-3/TrkC follows the same time course of expression as BDNF/TrkB. Immunostaining reveals that TrkB signaling may act mainly through satellite glia, Schwann cells, and supporting cells of Kölliker's organ, while TrkC signaling targets SGNs and pillar cells in humans. The NT-4 expression is upregulated when BDNF/NT-3 is downregulated, suggesting a balancing effect for sustained TrkB activation during fetal development. The mission of neurotrophins expects nerve fiber guidance, innervation, maturation, and trophic effects. The data shall serve to provide a better understanding of neurotrophic regulation and action in human development and to assess the transferability of neurotrophic regenerative therapy from animal models. [ABSTRACT FROM AUTHOR]

The aim of this study is to explore paroxetine's effect on nerve growth factor (NGF), human neurotrophin-4 (NT-4), and brain-derived neurotrophic factor (BDNF) levels in post-stroke depression. Ninety-two post-stroke depression patients from April 2021 to April 2023 in our hospital were selected and numbered 1 to 92 after enrollment. Forty-six patients with odd number and 46 patients with even number were, respectively, included in the control and observation group. In addition to basic treatment, control group was treated with flupentixol melitracen tablets orally, and observation group received paroxetine hydrochloride orally. The levels of NGF, NT-4, BDNF, 5-hydroxytryptamine (5-HT), homocysteine (Hcy), noradrenaline (NE), Hamilton Depression Scale (HAMD) changes of National Institute of Health Stroke Scale (NIHSS). NGF, NT-4, and BDNF levels were compared between groups at T0, T1, and T2 levels were higher, and the levels at T2 were higher than those at T1, and observation group levels were higher (P < 0.05); NGF, NT-4, and BDNF levels were compared among groups, time, and interaction. 5-HT, Hcy, and NE levels at T0 were compared between groups; 5-HT and NE levels at T1 and T2 were higher than those at T0, the levels at T2 were higher than those at T1, and observation group levels were higher (P < 0.05); Hcy level at T1 and T2 was lower, its level at T2 was lower than those at T1, and observation group levels were lower (P < 0.05); 5-HT, Hcy, and NE levels were compared among groups, time, and interaction (P < 0.05). HAMD and NIHSS at T0 were compared; T1 and T2 were lower than T0, T2 was lower than T1, and observation group was lower (P < 0.05); HAMD and NIHSS were compared among groups, time, and interaction (P < 0.05). For post-stroke depression, paroxetine treatment can effectively improve NGF, NT-4, BDNF, 5-HT, Hcy, and NE levels and effectively reduce the degree of neurological damage and depression, which has high clinical application value. [ABSTRACT FROM AUTHOR]

In orbital and ground-based experiments, it has been demonstrated that ionizing radiation (IR) can stimulate the locomotor and exploratory activity of rodents, but the underlying mechanism of this phenomenon remains undisclosed. Here, we studied the effect of combined IR (0.4 Gy γ-rays and 0.14 Gy carbon-12 nuclei) on the locomotor and exploratory activity of rats, and assessed the sensorimotor cortex volume by magnetic resonance imaging-based morphometry at 1 week and 7 months post-irradiation. The sensorimotor cortex tissues were processed to determine whether the behavioral and morphologic effects were associated with changes in neurotrophin content. The irradiated rats were characterized by increased locomotor and exploratory activity, as well as novelty-seeking behavior, at 3 days post-irradiation. At the same time, only unirradiated rats experienced a significant decrease in the sensorimotor cortex volume at 7 months. While there were no significant differences at 1 week, at 7 months, the irradiated rats were characterized by higher neurotrophin-3 and neurotrophin-4 content in the sensorimotor cortex. Thus, IR prevents the age-associated decrease in the sensorimotor cortex volume, which is associated with neurotrophic and neurogenic changes. Meanwhile, IR-induced increases in locomotor activity may be the cause of the observed changes. [ABSTRACT FROM AUTHOR]

Multiple sclerosis (MS) is a chronic, autoimmune neurodegenerative disease affecting the central nervous system. It is a major cause of non-traumatic neurological disability among young adults in North America and Europe. This study focuses on neuroprotective genes (BDNF, NT4/5, SIRT1, HSP70, and HSP27). Gene expression and protein levels of these markers were compared between MS patients and healthy controls. Blood samples were collected from 42 patients with multiple sclerosis (MS) and 48 control subjects without MS. Quantitative real-time PCR was performed to measure the expression of specific genes. The samples were analyzed in duplicate, and the abundance of mRNA was quantified using the 2-ΔCt method. ELISA assay was used to measure the concentration of specific proteins in the plasma samples. The results show that a 3.5-fold decrease in the gene expression of BDNF corresponds to a 1.5-fold downregulation in the associated plasma protein concentration (p < 0.001). Similar trends were observed with NT-4 (five-fold decrease, slight elevation in protein), SIRT1 (two-fold decrease, two-fold protein decrease), HSP70 (four-fold increase, nearly two-fold protein increase), and HSP27 (four-fold increase, two-fold protein increase) (p < 0.001). This study reveals strong correlations between gene expression and protein concentration in MS patients, emphasizing the relevance of these neuroprotective markers in the disease. [ABSTRACT FROM AUTHOR]

Abstract Background In-vitro-grow (IVG) of preantral follicles is essential for female fertility preservation, while practical approach for improvement is far from being explored. Studies have indicated that neurotrophin-4 (NT-4) is preferentially expressed in human preantral follicles and may be crucial to preantral follicle growth. Methods We observed the location and expression of Tropomyosin-related kinase B (TRKB) in human and mouse ovaries with immunofluorescence and Western blot, and the relation between oocyte maturation and NT-4 level in follicular fluid (FF). Mice model was applied to investigate the effect of NT-4 on preantral follicle IVG. Single-cell RNA sequencing of oocyte combined with cell-specific network analysis was conducted to uncover the underlying mechanism of effect. Results We reported the dynamic location of TRKB in human and mouse ovaries, and a positive relationship between human oocyte maturation and NT-4 level in FF. Improving effect of NT-4 was observed on mice preantral follicle IVG, including follicle development and oocyte maturation. Transcriptome analysis showed that the reparative effect of NT-4 on oocyte maturation might be mediated by regulation of PI3K-Akt signaling and subsequent organization of F-actin. Suppression of advanced stimulated complement system in granulosa cells might contribute to the improvement. Cell-specific network analysis revealed NT-4 may recover the inflammation damage induced by abnormal lipid metabolism in IVG. Conclusions Our data suggest that NT-4 is involved in ovarian physiology and may improve the efficiency of preantral follicle IVG for fertility preservation.

ABSTRACT Background and Objectives: Cerebral ischemia causes irreversible structural and functional damage in certain areas of the brain, especially in the hippocampus. The aim of this study was to examine effects of exercise preconditioning on neuronal cell death and expression of neurotrophin-4 (NT-4) and tropomyosin receptor kinase B (TrkB) in the hippocampal CA1 region following transient global cerebral ischemia/reperfusion in rat. Methods: Twenty-one male Wistar rats (weighing 250-300 g) were randomly divided into three groups (control+healthy, control+ischemia and exercise+ischemia). The rats in the exercise group ran on a treadmill five sessions a week for eight weeks. Ischemia was induced by occlusion of both common carotid arteries for 45 minutes. Cresyl violet staining was performed to assess cell death, and real-time PCR was carried out to evaluate expression of NT-4 and TrkB. Results: Cerebral ischemia was associated with significant neuronal death in the hippocampal CA1 region (P

Background: In-vitro-grow (IVG) of preantral follicles is essential for female fertility preservation, while practical approach for improvement is far from being explored. Studies have indicated that neurotrophin-4 (NT-4) is preferentially expressed in human preantral follicles and may be crucial to preantral follicle growth. Methods: We observed the location and expression of Tropomyosin-related kinase B (TRKB) in human and mouse ovaries with immunofluorescence and Western blot, and the relation between oocyte maturation and NT-4 level in follicular fluid (FF). Mice model was applied to investigate the effect of NT-4 on preantral follicle IVG. Single-cell RNA sequencing of oocyte combined with cell-specific network analysis was conducted to uncover the underlying mechanism of effect. Results: We reported the dynamic location of TRKB in human and mouse ovaries, and a positive relationship between human oocyte maturation and NT-4 level in FF. Improving effect of NT-4 was observed on mice preantral follicle IVG, including follicle development and oocyte maturation. Transcriptome analysis showed that the reparative effect of NT-4 on oocyte maturation might be mediated by regulation of PI3K-Akt signaling and subsequent organization of F-actin. Suppression of advanced stimulated complement system in granulosa cells might contribute to the improvement. Cell-specific network analysis revealed NT-4 may recover the inflammation damage induced by abnormal lipid metabolism in IVG. Conclusions: Our data suggest that NT-4 is involved in ovarian physiology and may improve the efficiency of preantral follicle IVG for fertility preservation. [ABSTRACT FROM AUTHOR]

Objective: Brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) are neurotrophins and they are critical regulators of the survival, differentiation, growth and plasticity of neuronal networks. There is plenty of evidence suggesting the involvement of altered levels of expression of neurotrophic factors in the pathophysiology of neuropsychiatric disorders. However, the relationship between neurotrophins and majör depression (MD) remains unclear. In this study, we assessed the relationship between the BDNF, NT-3, NT-4 gene expression levels in blood cells and MD. Methods: In a case-control study, total RNA was obtained from blood cells, 51 MD patients (diagnosed according to the DSM-5 criteria) and 75 healthy controls. Detected with quantitative Real Time PCR, expression levels of BDNF, NT-3, NT-4 genes were compared between the groups. Results: In this study, BDNF expression levels of the patients with MD were significantly higher than the control group but no statistically significant difference between NT-3 and NT-4 expression levels. There was no differences in expression levels of BDNF, NT-3 and NT-4 genes in MD patients with family history. There was no statistically significant difference in the BDNF, NTF-3 and NTF-4 expression levels among the sex groups for the patient group and no statistically significant difference between MD patients according to antidepressant usage time. Discussion: Not only in understanding the pathogenesis of MD but also in the follow-up of treatment, expression level changes of BDNF gene in blood cells of MD patients must be considered because of the bidirectional movement of BDNF between the periphery and the brain and effect of changing serum BDNF levels. [ABSTRACT FROM AUTHOR]

Background and Objectives: Cerebral ischemia causes irreversible structural and functional damage in certain areas of the brain, especially in the hippocampus. The aim of this study was to examine effects of exercise preconditioning on neuronal cell death and expression of neurotrophin-4 (NT-4) and tropomyosin receptor kinase B (TrkB) in the hippocampal CA1 region following transient global cerebral ischemia/reperfusion in rat. Methods: Twenty-one male Wistar rats (weighing 250-300 g) were randomly divided into three groups (control+healthy, control+ischemia and exercise+ischemia). The rats in the exercise group ran on a treadmill five sessions a week for eight weeks. Ischemia was induced by occlusion of both common carotid arteries for 45 minutes. Cresyl violet staining was performed to assess cell death, and real-time PCR was carried out to evaluate expression of NT-4 and TrkB. Results: Cerebral ischemia was associated with significant neuronal death in the hippocampal CA1 region (P<0.05). Exercise significantly decreased the ischemia-induced cell death (P<0.05). NT-4 expression was significantly lower in the control+ischemia group and in the exercise+ischemia group compared to the control+healthy group (P<0.05), but there was no significant difference between the control+ischemia group and the exercise+ischemia group in terms of NT-4 expression (P>0.05). Moreover, TrkB expression did not differ significantly between the groups (P>0.05). Conclusion: When used as a preconditioning stimulant before the induction of cerebral ischemia, exercise could have neuroprotective effects against cerebral ischemiainduced cell death, but it has no significant effect on NT-4 and TrkB expression. [ABSTRACT FROM AUTHOR]

Background & Objectives: Painful neuropathy is a state resulting from somatosensory disease or injury. Neurotrophins such as NT-4 are crucial for neural growth and development and protect the integrity of function and structure of nervous system. Paying heed to the importance of physical activity in neural plasticity, this study focuses on the investigation of chronic effect of decreased activity on the form of spinal nerve ligation on NT-4 gene expression of male Wistar rat’s sciatic nerve fiber. Materials & Methods: Ten adult male Wistar rats in the weight range of 250±30 gr were randomly divided into two groups, including one healthy control group (C) and one group with decreased physical activity (SNL). Over six weeks, neuropathic pain behavior tests were conducted continually in both groups. At the end of the sixth week, the changes in NT-4 gene expression in sciatic nerve were measured with Real time technique. Results: The behavioral tests demonstrated that spinal nerve ligation induced thermal hyperalgesia and mechanical allodynia in the SNL group. Decreased pain threshold was observed throughout the study period (p

Neurotrophins (NTs) belong to a family of trophic factors that regulate the survival, growth and programmed cell death of neurons. In mammals, there are four structurally and functionally related NT proteins, viz. nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 and neurotrophin 4. Most research on NTs to date has focussed on the effects of NGF and BDNF signalling via their respective cognate high affinity neurotrophic tyrosine kinase viz TrkA and TrkB receptors. Apart from the key physiologic roles of NGF and BDNF in peripheral and central nervous system function, NGF and BDNF signalling via TrkA and TrkB receptors respectively have been implicated in mechanisms underpinning neuropathic pain. Additionally, NGF and BDNF signalling via the low-affinity pan neurotrophin receptor at 75 kDa (p75NTR) may also contribute to the pathobiology of neuropathic pain. In this review, we critically assess the role of neurotrophins signalling via their cognate high affinity receptors as well as the low affinity p75NTR in the pathophysiology of peripheral neuropathic and central neuropathic pain. We also identify knowledge gaps to guide future research aimed at generating novel insight on how to optimally modulate NT signalling for discovery of novel therapeutics to improve neuropathic pain relief.

Background & Objectives: Painful neuropathy is a state resulting from somatosensory disease or injury. Neurotrophins such as NT-4 are crucial for neural growth and development and protect the integrity of function and structure of nervous system. Paying heed to the importance of physical activity in neural plasticity, this study focuses on the investigation of chronic effect of decreased activity on the form of spinal nerve ligation on NT-4 gene expression of male Wistar rat's sciatic nerve fiber. Materials & Methods: Ten adult male Wistar rats in the weight range of 250±30 gr were randomly divided into two groups, including one healthy control group (C) and one group with decreased physical activity (SNL). Over six weeks, neuropathic pain behavior tests were conducted continually in both groups. At the end of the sixth week, the changes in NT-4 gene expression in sciatic nerve were measured with Real time technique. Results: The behavioral tests demonstrated that spinal nerve ligation induced thermal hyperalgesia and mechanical allodynia in the SNL group. Decreased pain threshold was observed throughout the study period (p<0.05). Additionally, in comparison with the C group, NT-4 gene expression in sciatic nerve fiber was significantly higher in the SNL group (p<0.05). Conclusion: In the present study, it was discovered that the decreased activity in the form of SNL is associated with increased NT-4 gene expression in the experimental group. With respect to the physiologic functions of NT-4 in nervous system, this elevation is probably a mechanism for neurogenesis in the injured area, and based on the previous studies, it seems that the increased activity could enhance the increased NT-4 gene expression and accelerate neurogenesis. [ABSTRACT FROM AUTHOR]

Neurotrophins (NTs) belong to a family of trophic factors that regulate the survival, growth and programmed cell death of neurons. In mammals, there are four structurally and functionally related NT proteins, viz. nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 and neurotrophin 4. Most research on NTs to date has focussed on the effects of NGF and BDNF signalling via their respective cognate high affinity neurotrophic tyrosine kinase viz TrkA and TrkB receptors. Apart from the key physiologic roles of NGF and BDNF in peripheral and central nervous system function, NGF and BDNF signalling via TrkA and TrkB receptors respectively have been implicated in mechanisms underpinning neuropathic pain. Additionally, NGF and BDNF signalling via the low-affinity pan neurotrophin receptor at 75 kDa (p75NTR) may also contribute to the pathobiology of neuropathic pain. In this review, we critically assess the role of neurotrophins signalling via their cognate high affinity receptors as well as the low affinity p75NTR in the pathophysiology of peripheral neuropathic and central neuropathic pain. We also identify knowledge gaps to guide future research aimed at generating novel insight on how to optimally modulate NT signalling for discovery of novel therapeutics to improve neuropathic pain relief. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to determine the effect of low concentrations of advanced glycation end-products on neurite regeneration in isolated rat retinas, and to determine the effects of neurotrophin-4 on regeneration in advanced glycation end-products exposed retinas. Retinal explants of 4 adult Sprague-Dawley rats were cultured on collagen gel and were incubated in; (1) serum-free control culture media, (2) glucose-advanced glycation end-products–bovine serum albumin media, (3) glycolaldehyde-advanced glycation end-products–bovine serum albumin media, (4) glyceraldehyde-advanced glycation end-products–bovine serum albumin media, (5) glucose-advanced glycation end-products+neurotrophin-4 media, (6) glycolaldehyde-advanced glycation end-products+neurotrophin-4 media, or (7) glyceraldehyde-advanced glycation end-products+neurotrophin-4 supplemented culture media. After 7 days, the number of regenerating neurites from the explants was counted. Then, explants were fixed, cryosectioned, and stained for TUNEL. The ratio of TUNEL-positive cells to all cells in the ganglion cell layer was determined. Immunohistochemical examinations for the active-form of caspase-9 and apoptosis-inducing factor were performed. In retinas incubated with advanced glycation end-products containing media, the number of regenerating neurites were fewer than in retinas without advanced glycation end-products, and the number of TUNEL-positive cells and caspase-9- and apoptosis-inducing factor-immunopositive cells was significantly higher than in control media. Neurotrophin-4 supplementation increased the numbers of regenerating neuritis, and the number of TUNEL-positives, caspase-9-, and apoptosis-inducing factor-immunopositive cells were significantly fewer than that in advanced glycation end-products without neurotrophin-4 media. Low doses of advanced glycation end-products impede neurite regeneration in the rat retinas. Neurotrophin-4 significantly enhances neurite regeneration in retinas exposed to advanced glycation end-products. [Copyright &y& Elsevier]

In this study, we investigated the hypothesis whether neurotrophins have a differential influence on neurite growth from the entorhinal cortex depending on the presence or absence of hippocampal target tissue. We investigated organotypic brain slices derived from the entorhinal-hippocampal system to analyze the effects of endogenous and recombinant neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) on neurite outgrowth and reinnervation. In the reinnervation assay, entorhinal cortex explants of transgenic mice expressing enhanced green fluorescent protein (EGFP) were co-cultured with wild-type hippocampi under the influence of recombinant NT-3 and NT-4 (500 ng/ml). Both recombinant NT-3 and NT-4 significantly increased the growth of EGFP+ nerve fibers into the target tissue. Consistently, reinnervation of the hippocampi of NT-4−/− and NT-3+/−NT-4−/− mice was substantially reduced. In contrast, the outgrowth assay did not exhibit reduction in axon outgrowth of NT-4−/− or NT-3+/−NT-4−/− cortex explants, while the application of recombinant NT-3 (500 ng/ml) induced a significant increase in the neurite extension of cortex explants. Recombinant NT-4 had no effect. In summary, only recombinant NT-3 stimulates axon outgrowth from cortex explants, while both endogenous and recombinant NT-3 and NT-4 synergistically promote reinnervation of the denervated hippocampus. These results suggest that endogenous and exogenous NT-3 and NT-4 differentially influence neurite growth depending on the presence or absence of target tissue. [ABSTRACT FROM AUTHOR]

Abstract: We examined in adult Sprague Dawley rats the loss of retinal ganglion cells (RGCs) induced by complete intraorbital optic nerve crush (IONC) as well as the effects of several neurotrophic factors to prevent IONC-induced RGC loss. Completeness of the IONC lesion was assessed by investigating the orthograde and retrograde transport of neuronal tracers applied to the origin and termination of the retinotectal pathway. RGC survival after IONC alone or combined with intraocular injection of the neurotrophic factors NT-4, BDNF or CNTF was quantified at survival intervals ranging from 5 to 12 days post-lesion (dpl) by identifying RGCs that had been pre-labelled with fluorogold (FG). RGC loss first appeared at 7dpl and by 12dpl only 32% of the RGC population remained in the retina. Intraocular administration of NT-4, BDNF or CNTF resulted in almost a complete protection against IONC-induced RGC loss by 7dpl, and the protection remained significant by 12dpl only for NT-4 and BDNF. We have analyzed these results taking into account our previous studies on the loss of RGCs induced by intraorbital optic nerve transection (IONT) and concluded that RGC loss induced by IONC is slower and less severe than that following IONT. Moreover, as for IONT-induced RGC loss, IONC-induced RGC loss may also be prevented with administration of NT-4, BDNF or CNTF, though for NT-4 and CNTF their neuroprotective effects differ depending on the injury type. Overall this data underscore the importance of the type of ON injury on the pattern of RGC degeneration as well as in their response to neuroprotective treatments. [Copyright &y& Elsevier]

Abstract: Brain-derived neurotrophic factor (BDNF) is a member of the nerve growth factor (NGF) family and has been shown to promote neuronal survival and contribute to neural development. Although methylmercury, a neurotoxin, induces the cell death of neurons in vitro, there is little information regarding the effects of neurotrophins on the methylmercury-induced cell death of neurons. In the present study, we investigated the effect of BDNF on methylmercury-induced cell death in a primary culture of rat cerebellar granular cells. BDNF increased the viability of the cultured cells when treated alone, but unexpectedly accelerated the cell death induced by administration of methylmercury. Among other growth factors tested, only neurotrophin-4 (NT-4) demonstrated a similar acceleration of methylmercury-induced cell death. The cell death-accelerating effect of BDNF was inhibited by a BDNF-neutralizing antibody or a MAPK inhibitor. To determine whether the effect of BDNF occurs via TrkB, a receptor of BDNF and NT-4, we investigated the effects of BDNF and methylmercury in a TrkB transformant of rat neuroblastoma B35 cells. The methylmercury-induced cell death of the TrkB transformant was accelerated by BDNF, while that of the mock transformant was not. These results indicate that BDNF accelerates methylmercury-induced cell death via TrkB, at least in vitro, and suggest that BDNF and TrkB may also contribute to the sensitivity of neurons to methylmercury toxicity. [Copyright &y& Elsevier]

Abstract: Neurotrophins (NTs) appear to be crucial for the survival and potential regeneration of injured neurons. However, their temporal changes and remote regulations following spinal cord injury (SCI) have been only partially determined, especially in primates. In this study, ELISA was performed on the extracts of injured spinal cord and the associated precentral gyrus contralateral to the site of spinal cord hemisection to investigate the temporal changes in the levels of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3) and neurotrophin-4 (NT-4) in adult rhesus monkeys subjected to T8 spinal hemisection. Animals were allowed to survive 3, 7, 14, 30 and 90 days post-operation (dpo). In the spinal cord, the levels of NGF, BDNF and NT-3 sharply decreased between 3 and 7dpo. Thereafter, the levels of NGF and BDNF were transiently elevated while NT-3 level continuously increased and recovered to normal level at 30dpo. In the contralateral precentral gyrus (cPG), only the NT-3 level was altered and in fact elevated above the normal value. No obvious changes were observed in NT-4 level in any of the regions studied. Taken together, the present findings indicated that intrinsic NGF, BDNF and NT-3 may play a local role in the responses to the SCI in primates. Especially, the increase of NT-3 level occurred continuously in both the cPG and the spinal cord pointed to a possible transportation of NT-3 to the cord following SCI. [Copyright &y& Elsevier]

Abstract: The objective of the present study was to characterize the trkB receptor immunoreactive (-ir) cells in the intermediolateral cell column (IML) of the upper thoracic spinal cord. Small trkB-ir cells (area=56.1±4.4μm2) observed in the IML showed characteristics of oligodendrocytes and were frequently observed in close apposition to choline acetyltransferase (ChAT)-ir cell bodies. Large trkB-ir cells (area=209.3±25.2μm2) showed immunoreactivity for the neuronal marker NeuN, indicating their neuronal phenotype, as well as for ChAT, a marker for preganglionic neurons. TrkB and ChAT were co-localized in IML neurons primarily in cases that had received in vivo administration of nerve growth factor (NGF). These findings reveal two different cell types, oligodendrocytes and neurons, in the IML of the spinal cord that show trkB immunoreactivity, suggesting their regulation by brain derived neurotrophic factor (BDNF) and/or neurotrophin-4 (NT-4). In addition, there is evidence that NGF may play a role in the regulation of trkB-ir preganglionic neurons in the IML. [Copyright &y& Elsevier]

Neurotrophins (NTs), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), NT-3, and NT-4 are of major importance in prenatal and postnatal brain development, due to their neuroprotective action. Developmental changes alter the neuronal responsiveness to certain NTs, which subsequently are variously expressed, to properly balance their action. The following study aimed at examining the pattern of perinatal changes of the four NTs—NGF, BDNF, NT-3, and NT-4 in 30 appropriate for gestational age (AGA) full-term fetuses and neonates by determining their circulating levels at characteristic time points. This study show a gradual decrease of circulating levels of the NTs, NT-3 and NT-4 from umbilical cord (UC) to neonates day 4 (N4), while circulating levels of NGF and BDNF present the opposite pattern: an increase from UC to N4. These patterns of perinatal changes differ according to their impact on the process of neuronal development and their reaction to perinatal stress. NT3 and NT4 have been documented to act at early stages of neuronal development and to decrease after hypoxia-ischemia, while NGF and BDNF to increase. Further studies should investigate these patterns in premature or full-term infants, presenting various pathological conditions in the perinatal period. [ABSTRACT FROM AUTHOR]

The neurotrophin family of neurotrophic factors are well-known for their effects on neuronal survival and growth. Over the past decade, considerable evidence has accumulated from both humans and animals that one neurotrophin, nerve growth factor (NGF), is a peripheral pain mediator, particularly in inflammatory pain states. NGF is upregulated in a wide variety of inflammatory conditions, and NGFneutralizing molecules are effective analgesic agents in many models of persistent pain. Such molecules are now being evaluated in clinical trials. NGF regulates the expression of a second neurotrophin, brain-derived neurotrophic factor (BDNF), in nociceptors. BDNF is released when nociceptors are activated, and it acts as a central modulator of pain. The chapter reviews the evidence for these roles (and briefly the effects of other neurotrophins), the range of conditions under which they act, and their mechanism of action. [ABSTRACT FROM AUTHOR]

Abstract: Most fungiform taste buds fail to become innervated when BDNF or NT4 is overexpressed in the basal layer of tongue epithelium. Here, we examined when and how overexpression of BDNF and NT4 disrupt innervation to fungiform papillae. Overexpression of either factor disrupted chorda tympani innervation patterns either before or during the initial innervation of fungiform papillae. NT4 and BDNF overexpression each disrupted initial innervation by producing different gustatory axon morphologies that emerge at distinct times (E12.5 and E14.5, respectively). Chorda tympani nerve branching was reduced in NT4 overexpressing mice, and neuronal fibers in these mice were fasciculated and remained below the epithelial surface, as if repelled by NT4 overexpression. In contrast, many chorda tympani nerve branches were observed near the epithelial surface in mice overexpressing BDNF, and most were attracted to and invaded non-taste filiform papillae instead of gustatory papillae. These results suggest that BDNF, but not NT4, normally functions as a chemoattractant that allows chorda tympani fibers to distinguish their fungiform papillae targets from non-gustatory epithelium. Since BDNF and NT4 both signal through the p75 and TrkB receptors, trophin-specific activation of different internal signaling pathways must regulate the development of the distinct gustatory axon morphologies in neurotrophin-overexpressing mice. [Copyright &y& Elsevier]

Abstract: The transmembrane tyrosine-specific protein kinase TrkB has been shown to serve as a receptor for the neurotrophic factors BDNF and NT-4. Neurotrophin binding to TrkB isoformes mediates many intracellular signaling pathways, including calcium signalling. Two truncated isoforms of the receptor, lacking the tyrosine kinase activity, signal through a yet unknown pathway. Specific signals modulate the surface expression of TrkB, which is localized in considerable amounts in intracellular pools. These intracellular pools has not been specified so far. We therefore investigated the intracellular distribution of TrkB by colocalisation studies. In contrast to the unspecific neurotrophin receptor NGFRp75, TrkB immunohistochemistry showed a staining pattern very similar to mitochondrial stainings in adult human skeletal muscle fibers. Immunofluorescence techniques revealed in different types of permeabilized cells that TrkB is bound to mitochondrial membranes. This observation was confirmed on isolated astrocyte mitoplasts. Colocalisation of the TrkB ligand NT-4 and the specific mitochondrial marker cytochrome c oxidase was also observed. Western blot analysis of isolated mitochondria from rat brain and skeletal muscle verified that a truncated isoform of TrkB is present in both, brain and muscle mitochondria, and full-length TrkB is additionally present in brain mitochondria. Our results imply that neurotrophins can be stored in mitochondria and possibly act as signalling molecules on mitochondria. [Copyright &y& Elsevier]

Neurotrophins (NT5) such as BDNF, NT-3, and NT-4 are important modulators of neuronal function and survival. Their expression in the CNS after various insults is thus of major therapeutic consequence. Glatiramer acetate [(GA) Copaxone), an approved drug for the treatment of multiple sclerosis, has been shown to induce Th2/3 cells that accumulate in the CNS, expressing in situ antiinflammatory cytokines and BDNF. In the present study, we investigated whether s.c. injections of GA, applied at various stages of experimental autoimmune encephalomyelitis, affect the expression of NT5, particularly BDNF, in the brain. In untreated experimental autoimmune encephalomyelitis mice, the expression of NTs was elevated shortly after disease appearance but subsequently declined below that of naive mice. In contrast, GA treatment led to sustained augmentation in the expression of BDNF. NT-3, and NT-4 in various brain regions as demonstrated by histological analysis of immunostained brain sections. GA treatment, even when started 45 days after disease induction, restored the impaired level of NTs to that of healthy mice. BDNF elevation after GA treatment was demonstrated on both protein and mRNA levels. Prominent staining was manifested not only by infiltrating GA-induced T cells, but also by CNS resident cells (neurons and astrocytes), indicative of a bystander therapeutic effect. Of importance, in GA-treated mice, intense BDNF expression was manifested by neuronal progenitors that migrated into lesions in injured regions. These results indicate that the immunomodulator GA exerts not only an antiinflammatory effect, but also enhances neuroprotection and regeneration of neural elements in the diseased brain. [ABSTRACT FROM AUTHOR]

The changes in the expression of brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4) in the rat neuromuscular system as a result of three different types of sciatic nerve injuries have been evaluated. The changes in mRNA and protein levels for BDNF, NT-3, and NT-4 in the soleus muscle and sciatic nerve were assessed 4–28 days after sciatic nerve transection (neurotmesis), sciatic nerve crush (axonotmesis), and mild acute compression (neurapraxia). BDNF mRNA levels increased dramatically with nerve transection in the soleus muscle and the sciatic nerve 7–14 days after injury, whereas the changes were low in other types of injury. The changes of protein levels for BDNF were also similar. The mRNA and the protein levels of NT-3 in the soleus muscle did not show any significant difference. The mRNA for NT-4 in the soleus muscle decreased from 4 to 14 days after sciatic nerve transection, and the protein level was also minimum 14 days after sciatic nerve transection. Our results indicate that the neurotrophic factors in the neuromuscular system could play a role in differentiating peripheral nerve injury. [ABSTRACT FROM AUTHOR]

Neurotrophins are a family of secreted neuronal survival and plasticity factors comprising NGF, BDNF, neurotrophin-3 (NT-3), and NT-4. Whereas synaptic secretion of BDNF has been described, the routes of intracellular targeting and secretion of NGF, NT-3, and NT-4 in neurons are poorly understood. To allow for a direct comparison of intracellular targeting and release properties, all four mammalian neurotrophins were expressed as green fluorescent protein fusion proteins in cultured rat hippocampal neurons. We show that BDNF and NT-3 are targeted more efficiently to dendritic secretory granules of the regulated pathway of secretion (BDNF, in 98% of cells; NT-3, 85%) than NGF (46%) and NT-4 (23%). For all NTs, the remaining cells showed targeting to the constitutive secretory pathway. Fusing the BDNF pre-pro sequence to NT-4 directed NT-4 more efficiently to the regulated pathway of secretion. All neurotrophins, once directed to the regulated secretion pathway, were detected near synapsin I-positive presynaptic terminals and colocalized with PSD-95-DsRed (postsynaptic density-95-Discosoma red), suggesting postsynaptic targeting of the neurotrophins to glutamatergic synapses. Depolarization-induced release of all neurotrophins from synaptic secretory granules was slow (delay in onset, 10-30 s; τ = 120-307 s) compared with transmitter release kinetics monitored with FM4-64 [N-(3-triethylammoniumpropyl)-4-(6-(4-diethylamino)phenyl)hexatrienyl)pyridinium dibromide] destaining (onset, <5 s; τ = 13 ± 2 s). Among the neurotrophins, NT-4 secretion was most rapid but still proceeded 10 times more slowly than transmitter secretion. Preincubation of neurons with monensin (neutralizing intragranular pH, thus solubilizing the peptide core) increased the speed of secretion of BDNF, NGF, and NT-3 to the value of NT-4. These data suggest that peptide core dissolution in secretory granules is the critical determinant of the speed of synaptic secretion of all mammalian NTs and that the speed of release is not compatible with fast transmitter-like actions of neurotrophins. [ABSTRACT FROM AUTHOR]

Abstract: Almost all sensory neurons of the dorsal root ganglia have a mechanosensitive receptive field in the periphery. We have shown that the sensitivity to mechanical stimuli of a subset of sensory neurons that are slowly adapting mechanoreceptors (SAM) is strongly dependent on the availability of brain-derived neurotrophic factor (BDNF). Here we have investigated whether the ASIC2 sodium channel, recently shown by us to be necessary for normal SAM sensitivity, might be regulated by BDNF and thus partially account for the down-regulation of SAM sensitivity seen in BDNF deficient mice. We show that the mRNA for ASIC2 channels is reduced in the DRG of BDNF deficient mice indicating that BDNF might maintain its expression in vivo. We also made short-term cultures of sensory neurons from adult BDNF deficient mice and used a specific antibody to detect the presence of ASIC2 channels in different classes of sensory neurons. We observed that the channel protein was dramatically down-regulated selectively in medium and large diameter neurons and this expression could be rescued in a dose and time dependent manner by addition of BDNF to the culture (10–100 ng/ml). Drugs that block new transcription or protein synthesis also prevented the rescue effects of BDNF. We observed that ASIC2 channels were down-regulated in sensory neurons taken from neurotrophin-4 and neurotrophin-3 deficient mice; these effects might be due to a selective loss of neurons that normally express large amounts of ASIC2 channels. In summary, our data identify the ASIC2 channel as a target of BDNF signaling in vivo and suggest that the functional down-regulation of sensory mechanotransduction in BDNF deficient mice is in part due to loss of ASIC2 expression. [Copyright &y& Elsevier]

The principal glucocorticoid in rats, corticosterone, interacts with neurons in the limbic system and leads to morphological and behavioral changes. Putative corticosterone-triggered mediators are neurotrophins. In the present study we investigated the effects of early postnatal corticosterone treatment in rats on neurotrophic factors of the nerve growth factor (NGF) family and their receptors. Newborn rats were treated with corticosterone-containing polymers until postnatal day 12. The mRNA and protein levels of the neurotrophins of the NGF family (NGF, BDNF, NT-3 and NT-4/5) and their receptors (trkA, trkB, trkC and p75) were quantified in septum and hippocampus using RT-PCR. In the septal region, we found an unchanged mRNA expression after corticosterone treatment, whereas in the hippocampus there was a general increase in mRNA. Particularly, the gene expression of NGF, NT-3, and the high affinity receptors trkA, trkB and trkC increased significantly. Quantification of the neurotrophin protein levels using an ELISA revealed significant treatment effects for NGF and NT-4/5 in the hippocampus. The present study of corticosterone treatment in young rats demonstrates interactions of steroid hormones with neurotrophic factors and their receptors in the septo-hippocampal system during the first two postnatal weeks. [ABSTRACT FROM AUTHOR]

The neurotrophins, a class of four related growth factors, utilize a dual receptor system consisting of Trk receptor tyrosine kinases and the structurally unrelated p75NTR to modulate diverse and sometimes opposing biological actions. The identification of novel ligands for p75NTR, unconventional mechanisms for Trk activation and unique signaling intermediates further underscores the complex nature of neurotrophin: receptor interactions, as well as their functions within and outside of the nervous systems. This review summarizes recent surprises of how ligand-receptor pairing may affect diverse developmental events, regulate response to injury and extend their influence on memory and learning. [ABSTRACT FROM AUTHOR]

Microglia are thought to play a key role in the development and regeneration of the central nervous system although the mechanisms regulating their presence and activity are not fully understood. Substantial evidence suggests that members of the neurotrophin family such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 and -4 (NT-3/4) have a dramatic effect on both neurons and perineuronal cells. This study employed two murine microglial lines, BV-2 and N9, to examine the action of these neurotrophins on the mitotic activity and survival of microglia in vitro. Neurotrophins were incorporated into the media at the time of plating and cell number and levels of mitochondrial dehydrogenase activity (MTT) were determined at various time points in vitro. NGF increased cell number and MTT levels of both cell lines in a dose-dependent manner. BV-2 was more sensitive to NGF than N9. Similar responses were elicited by BDNF, although the sensitivity of each cell line was different than that found for NGF. NT-3 and NT-4 had no effect on cell proliferation. However, NT-4 had an effect on the survival of BV-2 and N9 cells. The response of these cells to neurotrophins was blocked by K252a, a tyrosine kinase inhibitor, suggesting that actions of neurotrophins were mediated by high-affinity tyrosine kinase receptors (Trk). Immunolocalization studies revealed positive Trk (pan) reactivity in the above cell lines and in primary microglia, but an absence of the low-affinity p75 neurotrophin receptor. Western blot analysis supported the above observations. These studies suggest that in addition to their neurotrophic actions, NGF and BDNF may also regulate microglial dynamics, thereby influencing the surrounding milieu during neuronal regeneration. [Copyright &y& Elsevier]

Neurotrophins are potent regulators of neuronal survival, maintenance, and synaptic strength. In particular, brain-derived neurotrophic factor (BDNF), acting through full-length TrkB receptor (TrkBFL), is implicated in the stimulation of neurotransmission. Physical activity has been reported to increase BDNF expression in the brain and spinal cord. In this study we have evaluated the hypothesis that activation of a spinal neuronal network, due to exercise, affects the entire spinal neurotrophin system acting via TrkB receptors by modulation of BDNF, neurotrophin 4 (NT-4), and their TrkB receptor proteins. We investigated the effect of treadmill walking (4 weeks, 1 km daily) on distribution patterns and response intensity of these proteins in the lumbar spinal cord of adult rats. Training enhanced immunoreactivity (IR) of both neurotrophins. BDNF IR increased in cell processes of spinal gray matter, mainly in dendrites. NT-4 IR was augmented in the white matter fibers, which were, in part, of astrocytic identity. Training strongly increased both staining intensity and number of TrkBFL-like IR small cells of the spinal gray matter. The majority of these small cells were oligodendrocytes, representing both their precursor and their mature forms. In contrast, training did not exert an effect on expression of the truncated form of TrkB receptor in the spinal cord. These results show that both neuronal and nonneuronal cells may be actively recruited to BDNF/NT-4/TrkBFL neurotrophin signaling which can be up-regulated by training. Oligodendrocytes of the spinal gray matter were particularly responsive to exercise, pointing to their involvement in activity-driven cross talk between neurons and glia. [Copyright &y& Elsevier]

Levels of mRNA for neurotrophins (brain-derived neurotrophic factor, BDNF; neurotrophin 3, NT-3; neurotrophin 4, NT-4) and their receptors ( trkA, trkB, trkC) and for glial cell line-derived neurotrophic factor (GDNF) and its receptors ( ret, GDNFR-α) were measured in rat thyroid tissue by ribonuclease protection assays. In thyroid tissue the NT-3 mRNA level was threefold lower and the NT-4 mRNA level sixfold higher than those detected in adult rat hippocampus, while BDNF mRNA was undetectable. Very low levels of mRNA for truncated trkB and trkC receptors and no catalytic trkA, trkB or trkC were found. In conclusion NT-3 and NT-4, but not the corresponding functional receptors, are expressed in the thyroid tissue. Therefore, it is unlikely that these factors serve a direct local autocrine or paracrine function in thyroid cell types, and a target-derived mode of action on neurons innervating the thyroid tissue is suggested. An opposite result has been found for the neurotrophic factor GDNF: thyroid tissue showed a high level of transcripts for the GDNF receptor subunits (GDNFR-α and Ret), while GDNF mRNA was undetectable. The in situ hybridization analysis of GDNFR-α and ret mRNA revealed an interesting difference in the cell distribution of these transcripts: ret mRNA is selectively expressed in a subpopulation of cells scattered in the follicular epithelium and in the interfollicular spaces, while GDNFR-α expression is more homogeneous and widespread, including the more abundant cell type of the thyroid gland: the follicular cell. Double-labeling in situ hybridization/immunocytochemistry experiments, with a specific marker (calcitonin), showed that parafollicular cells express ret but not GDNFR-α. This differential distribution of the GDNF receptor components (GDNFR-α and ret) may reflect a peculiar biological role in intercellular communication in the thyroid gland. [ABSTRACT FROM AUTHOR]

The purpose of this study was to explore the antidepressant-like effects of vitamin D3 at different doses (1.0, 2.5, and 5.0 mg/kg sc) on a model of depression produced by chronic unpredictable mild stress (CUMS) for 28 days in long-term (3 months) ovariectomized (OVX) adult rats. Sucrose preference (SPT), forced swimming (FST) and open-field (OFT) tests were conducted to examine the depression-like state. Serum corticosterone/adrenocorticotrophic hormone (ACTH) levels and hippocampal brain-derived neurotrophic factor (BDNF) and neurotrophin (NT)-3/NT-4 expressions by ELISA kits and/or western blotting were determined to assess the possible mechanisms of the vitamin D3 effects on the depression-like profile in long-term OVX rats subjected to CUMS. The results showed that vitamin D3 (5.0 mg/kg), as well as fluoxetine treatment, considerably reversed the depression-like state in the SPT and FST, decreased serum corticosterone/ACTH levels, and increased BDNF and NT-3/NT-4 levels in the hippocampus of long-term OVX rats compared to OVX rats with CUMS (p < 0.05). Thus, a high dose of vitamin D3 (5.0 mg/kg sc) could improve the depression-like profile in long-term OVX adult female rats subjected to the CUMS procedure, which might be mediated by the regulation of BDNF and the NT-3/NT-4 signaling pathways in the hippocampus, as well as the corticosterone/ACTH levels of the blood serum. [ABSTRACT FROM AUTHOR]